Method of bonding



June 2, 1953 N. LANGER METHOD OF BONDING Filed March-2e, 1952 Patented June 2, 1953 UNITED STATES PATENT OFFICE METHOD F BONDING Nicholasv Langer, New York, N. Y.

Application March 26, 1952, Serial No'. 278,570

11l Claims.

This invention relates to machines andi methods for bondingI or sealingk togethery a plurality off pliesv or layers of thermoplastic sheet material. Thepresent applica-tion is a -continuation-inpart ofmyco-pending application Serial No. 21.23886, filed'February 27, 1951.

In recent yea-rs Various bonding machines-have been introducedI for bonding together plies of thermoplastic material by localized heating of the material through the spacey between al pair ofj electrodes connected to a sourceoif radiofrequencyA energy, thedisplacement of suoliYV plies being effected in a step-by-step or discontinuous mannen such as in a conventionali sewingJ machine, or inA a continuous manner, suchas by means of a pair of feed rolls. The powerful high frequency eld producedin the electrodey Zone willi heat upthe pliesy ofv the material passing therethrough to -theirbonding temperature; cans ing sealing or bonding ofl such plies as aresult offthe'joint effect of heat and'V electrode pressure.

Whilel electrostatic bonding machines of the described character, sometimesy referred to as electronic sewing machines, have been used. in the` industry for somey year-szon a ratifier4 limited scale, their use onk a large scale in thel quantity production of articles formed from: thermoplastic sheet" materials was seriously han'dicappedf and in manyy cases was completely. preventedl by' a combination ofi the following factors:l

(1)A The operation ofv conventional electronic sewing machinesv isV based; on. the heat. produced in the material as a resultv of dielectric losses in a= high frequency ii'eldl This introduces', certain limitations as` to the typesiof,` thermoplastic. ma terial's: whichf may besuccessfully bonded-1 and obviously' excludes such. materials irrl which the dielectricA losses areiveryflow'. It so happenslthat therearevarious materials, such asparticularly polyethylene; which' are characterized by an extremely. W loss factor, although they are quite desirable for'other reasons; such asl'ow` oost; high strength, chemical' inertness, low gas permea' bility, and the like.

(21) In viewy of" the extremely high frequencies usedl in conventional electronic bonding: ma chines, serious problems are introduced in connectionwith impedance matching; in: controlling the amount of heat generatedA inthe plies, etc. EvenA very minute and frequentlyl unavoidable variations inthe composition and.` thickness of the plies orin the rate at which'the-pliesarefed past the bonding electrodes may" prevent the production off' uniformly' sound sealsZ orV bonds. The adjustment oi` electrode spacing is quit'eicrii- 2 tical andA even with, themost. carefulv adjustment it is next toy impossible to bondzveryV thin: layers ory plies which are frequently overheatedA or burned rather than properly sealed.

(3)y The amount of high frequency` energy* required isquite considerable. and the equipment for generating such energy is bulky. and alsoexpensive both to build and to operate. As azresult, the initial cost of these electronic bonding4 machines is quite high andv their commercialpuseds profitable only in extreme casesV Where no other method of heat sealing or bonding will servez,

I have discovered that the outstanding. problem mayr be solved` andi the:Y foregoing; disadvantages may be eliminated: in.. a. remarkably4 simple 11184D1161,

It` is anL object, ofi' the present invention-1 to im.'- prove electronic bonding: machines.`

I-tA isL another object of the; present invention to provide a novelA and:` improved electronic; hondingA machine and; method.V

It is: ai further object" off, thef present, invention toprovide a nouelmachine; andlmethodfon bonding togetherI plies,r oli' thermoplastic sheet, mate'- rial inn which a progressively displaced, filamentary member isk combinediwith linear, regions of the pliesy to cause transfer or, sealing; heat thereto; and permanent bonding of, the; plies, in corresponding regions;

It is. also within; the` contemplation ot thev invention to; provide.- an electronicbonding machine which; requires onlyvery small.I amounts ofk high frequency energyf'for its satisfactory operation.`

Theinyention also contemplates annelectronio bonding: machine which; is:r simple and. inexpensive to:` construct and. tov1 operate andi which may bei manufactmaed: andi` soldv at a fraction of. the cost of conventional electronic bondingmachines.

@ther and furtl'rer` objectsl and` advantages of the inventionawillihecome apparent fromv thepfollowing. description, takerr innconjunctionlwith the accompanying drawing; in: which:-

Figure 1'1 is:v ai side eleyatiom somewhatdiagrammaticY and, fragmentaryj in character,r and having parts in section, of: anelectronic bonding machine embodying the principlesy ofv the present invention;

Figurev Z'isia: front View, of: aportion ot thelmaf chine' showna in'lligure 13;

Figure 3`L is arfragmentaryf'top plarn vieiwofz two layers@ of," thermoplastic sheet, material, bonded iiilr'igether in*- accordance; with` my presenti' ini/,env-

Figura 41- is a: section. takenf. onf line-f of, urei3 andi Figure is a View similar to Figure 1, also diagrammatic and fragmentary in character, of a modified embodiment of the present invention.

Broadly considered, in accordance with the principles of my invention, the layers or plies of thermoplastic sheet material to be bonded together are brought into contact with a filamentary member, such as a lament, thread, wire, strip or narrow band, which is preheated to a temperature at least equaling but preferably somewhat exceeding the bonding temperature of the layers. The structure constituted by said layers and said lamentary member is then passed through a pressure zone wherein a limited length of the structure is placed under compression. This compression and the intimate contact and heat exchange relation between the preheated lamentary member and the underlying layers will cause the transfer of bonding heat from the said member onto the said layers. The combined eect of heat and pressure in the pressure zone will cause heat sealing or bonding of the layers in a corresponding linear region, at the same time partially or fully embedding the lamentary member in the bonded region, thereby `producing a lengths of the thermoplastic layers with the complished by passing the same through a heating zone wherein the said member is exposed to the effect of suitable heating means. These heating means may be of a greatly different char- 'acter in accordancewith the material of the la- "mentaiy member and the specific requirements of the particular machine. For example, good results may be obtained by radiant heating means to which the filamentary member is exposed or by hot gases impinged against the member. It is preferred, however, to utilize a high frequency electrostatic or electromagnetic field through 'which the lamentary member is passed immedlately before it is combined with the layers of thermoplastic material. It is also possible and is in some cases advantageous to combine the preheating and the pressure-applying or bonding `zone into a common zone in which both the preheating as well as the bonding will take place whereby the heat losses in the interval that will elapse before the bonding heat stored in the filamentary member is transferred to the layers to be lbonded together are substantially completely eliminated. Q

Referring now more particularly to Figures 1 'and 2 of the drawing, reference numerals I0 and 'II denote a pair of rotatable pressure rolls or wheels between which the layers of thermoplastic 'material I2 and I4 may be advanced with the assistance of a feed table I5. A filament I6 of a suitable material is unwound from a spool or roll I'I and is guided around the lower circumferential surface of roll IIJ to be deposited onto the upper surface of layers I2 and I4. Between spool I1 and upper pressure roll ID, the length of the filament -is exposed to the heating effect of a high frequency lfield, such eld being produced in the axial space 4of a coil I8 of a few turns or in the space between a pair of electrodes I9. Coil I8 or electrodes I9 are energized with high frequency energy from a generator 20. The output of generator is connected to the switching arms 2I and 22 of a double pole-double throw switch 23 by conductors 24 and 25 respectively. The working contacts of the said switch 26, 21 and 28, 29 are connected to the respective ends of coil I8 and electrodes I9. Thus, it will be noted that by manipulating switch 23, either coil I8 or electrodes I9 will be energized by the output of generator 20. In general, where the filamentary member is formed of an electrically conducting material, it is preferred to employ the heating effect of the high frequency electromagnetic eld in the axial space of coil IB, while the heating effect of the high frequency electrostatic field between electrodes I9 is relied upon for preheating the filamentary member I6 when the said member is formed of a non-conducting or dielectric material. As it will be best observed in Fig. 2, a shallow groove 30 is provided in the circumferential surface of roll I0 in order to assure more positive guiding of the filamentary member around the said roll.

From the foregoing description, the operation of the machine of the invention will be readily understood by those skilled in the art. When it is desired to operate the machine, the leading edge of layers I2, i4, together with the free end of filament IS is introduced into the bight of rolls I0 and I I and the said rolls are rotated in the direction of arrows 3I and 32 by means of any suitable driving mechanism (not shown) Switch 23 is placed into its upper or lower position in accordance with the circumstance whether the heating effect of an electromagnetic or of an electrostatic high frequency field will be relied upon, this being, of course, largely determined by the material of the filament.

During the operation of the machine, the filament IB is being continuously drawn from spool I'I through heating zones or stations represented by coil I8 or electrodes I9 whereby successive lengths of such filaments are progressively preheated at least to the bonding temperature of layers I2 and I4. These preheated portions of the filament are then pressed against the under lying region of layers I 2 and I 4 by means of pressure rolls IIJ and II whereby the bonding heat stored in the filament is transferred onto such region, causing permanent bonding thereof in a corresponding linear region by the combined effect of heat and pressure thereon. The heating effect of the high frequency heating means, (coil I8 or electrodes I9), is so correlated to the speed of advancing the layers through the rolls I and II that even after the unavoidable heat losses caused by the period elapsing between the preheating step and the pressing step, still sufficient heat remains in the filament to produce a satisfactory bond. In general, this requires preheating the lament to a temperature which at least equals but in most cases substantially exceeds the actual bonding temperature of the layers.

Figs. 3 and 4 illustrate the appearance of the bonded product of the machine shown in Figs. 1 and 2. It will be noted that the product comprises a pair of layers I2 and I4 of thermoplastic material which are fused together in their interface along a linear region 33, corresponding vto the region directly underlying filament I6.

The said filament is partially or fully embedded into one or both of the said layers and in most cases is likewise permanently secured and is made integral with the bonded product. It is entirely feasible, however, to carry out the method of the invention in such a manner as to have the filament embedded into the bonded product only to a very slight extent so that it can be readily stripped from the bonded layers after the bonding operation has been completed. In this case, the filament merely serves for transferring the bonding heat from the heating Zone onto the regions to be bonded and is discarded after the bonding operation which may provide special advantages in certain practical applications of the invention.

Great variations are possible in the material of theiilamentary member I6. If an electrically conducting member is desired, one which is preferably preheated by means of a high frequency electromagnetic field, this member may be in the form of a thin, highly flexible metal wire or band having at least fair mechanical strength, such as copper, aluminum, steel or iron wire, strip, or band. Other materials suitable for the purposes of the present invention are synthetic laments of an electrically conducting character, such as filaments extruded from cellulose derivatives, rubber hydrochloride, vinyl resins, vinylidene chloride, or polyethylene. These materials, which are normally good dielectrics, are rendered electrically conducting by the incorporation of sewing thread through a colloidal graphite solution, such as the colloidal graphite preparation known under the name Aquadag or by impregnating or coating the thread with such preparation in some other suitable manner.

If yan electrically non-conducting or dielectric filamentary member is desired., one which is preferably preheated by means of a high frequency electrostatic eld, this member may be in the form of a thin and flexible filament,

thread, band or narrow strip of a suitable plastic, advantageously one in which the dielectric losses are relatively high. Examples of such plastics are various cellulose derivatives, vinyl resins, vinylidene chloride, and the like. if the plastic is of such character as to have an undet sirably low loss factor, such loss factor may conveniently be increased to the exact value red by the incorporation of conducting particles. In most cases such conducting particies are incorported in amounts sufcient to increasel the loss factor to the desired extent but insuiiicient to render the filament actually conducting. Conventional sewing thread is also useful for the `purposes of electrostatic preheating as the natural moisture content thereof is generally suincient to cause its heating to the desired bonding temperatures without requiring any special impregnating or coating treatment. Generally speaking, the material of the filament is selected as to have a melting or softening point which is considerably higher than that of the thermoplastic layers tobe bonded in order to prevent excessive weakening thereof during the preheating step.

Figure illustrates diagrammatically a modified bonding machine embodying the invention which is in many respects similar to the machine described in connection with Figures l and 2 but has the advantage of bringing the preheating zone closer to the pressure applying or bonding zone. In this figure, similar reference numerals have been used to denote corresponding parts that are present in the machine of Figures 1 and 2.

Referring now to Figure 5, a filament I6I of dielectric material is unwound from roll or spool Il and is passed around pressure roll lil cooperating with another pressure roll Il. Layers l2 and i4 of thermoplastic material are fed: into the bight of rolls iD and Il along feed table l5"- and are brought into contacting position with the superimposed filament I6. An electrode roll 34 is pressed against the circumferential surface of roll l0, into contact with filament i6 wound therearound. A source of high frequency energy 2G has one of its output terminals connected to roll I9 through a conductor 35, while the other `output terminal of said source is connected through a conductor 36 to a switching arm 3l of a switch having operating contacts 3S and 3B.. Contacts 38 and 39 are connected to rolls 3Q and il by means of conductors 40 and M, respectively. It will be notedr that a high frequency electrostatic field will be established between rolls Ill and itil, or between rolls Hi andv l-l, respectively7 in accordance with the position of switch Si.

ln view of the similarity of construction, the operation of this modified embodiment of theinvention will be readily .understood without any detailed description. It will be sufficient to state that when the operation of the machine is initiated and rolls it and Il are rotated by the drn ing mechanism (not shown), filament i6. of dielectric material is` drawn from spool il andvis brought into superimposed position with respect to layers it and it. In the left hand position. of switch the high frequency field will be established between rolls IllV and 34, causing preheatof the filament immediately before the said filament enters the bight of pressure rolls I0 and li. Thus, the successive preheated portions of filament it are pressed against the underlying thermoplastic layers i2 and l before their temperature is reduced by radiation, or heat. losses due to other factors. In the right hand position of switch 3l', roll 34 merely serves yas a guide roll and the high frequency field is established between the pressure rolls Hl and liy themselves, thus renderingthe preheating step practically coincidental with the pressure-applying step. In the latter case, it is desirableto form the filament i6 of a relatively high-loss dielectric material, such as of a suitable vinyl resin, and to form the layers to be bonded together from relatively low-loss thermoplastic dielectric material, such as polyethylene. This will assure thatk most of the dielectric losses will be produced in the fila.- inent itself whereas the heating of the underlying layers to be bonded together will be the result of heat transfer between the preheated filament and the layers, rather. than the direct result of dielectric losses in the layers.

.It will be noted. that the principles of the present invention provide numerous advantages, the most important of which are the following:

(l) Since the sealing heat is generated inl a filamentary member of greatly reduced cross section, rather than in the thermoplasticy 4layers themselves, the high frequency power requirements are a mere fraction of those of conventional electronic bonding machines.

(2) The control of the sealing heat is greatly facilitatedr and the quality and strength of the resultingV bond is not markedly influenced by small variations in the thickness of the layers to be bonded. Good bonds may be obtained even when the number of 1ayers or plies is different along different portions of the linear seam.

(3) The problem of impedance matching between the high frequency generator and the heating coil or electrodes is greatly simplified.

(4) When the material of the filament remains the same, the adjustment of the high frequency circuit is not appreciably affected by a change in the material or in the thickness of the layers to be bonded, provided that the amount of heat stored in the filament during the preheating step is adequate for bringing the underlying layers to their bonding temperature.

(5) The invention makes it possible to readily seal thermoplastic layers of a material in which the dielectric losses are extremely low, such as polyethylene. As is known, heretofore it was not possible to seal such thermoplastic materials by means of conventional electronic bonding machines.

(6) The invention permits the sealing of thermoplastic layers of very low thickness. Such thin layers could not be bonded with conventional machines due to the extremely critical adjustment of the high frequency power output which would frequently cause burning or destruction of the thin layers without producing an adequate bond.

Although the present invention has been described in connection with a few preferred embodiments thereof, variations and modifications may be resorted to by those skilled in the art without departing from the principles of the invention. I consider all of these variations and modifications to be within the true spirit and scope of my invention, as disclosed in the foregoing description and defined by the appended claims.

What is claimed is:

l. The method of heat sealing layers of thermoplastic material which comprises bringing regions of the layers to be heat sealed into face-toface superposed position, preheating an elongated member to heat sealing temperature in the absence of Contact with the layers to be sealed, and pressing said preheated member against said regions of the layers to cause heating and bonding of said member and of said layers in such regions.

2. The method of heat sealing layers of thermoplastic material which comprises bringing regions of the layers to be heat sealed into face-toface superposed position, progressively preheating successive portions of an elongated member to heat sealinov temperature in the absence of contact with the layers to be sealed, and progressively pressing the preheated portions of said member against said regions of the layers to cause heating and bonding of said member and of said layers in a linear seam.

3. The method of heat sealing layers of thermoplastic material which comprises progressively preheating successive portions of an elongated filamentary member to heat sealing temperature in the absence of contact with the layers to be sealed, and progressively pressing such preheated portions of said member against said layers to cause heating and bonding of said member and of said layers in a corresponding linear region.

4. The method of heat sealing layers of thermoplastic material which comprises progressively passing a iilamentary member through a heating zone to preheat said member to a temperature at least equaling the bonding temperature of the layers in the absence of contact with such 1ayers, and progressively pressing preheated portions of the member against said 1ayers to cause permanent bonding of said member and of the underlying layers into a single heat sealed structure in a corresponding linear region.

5. The method of heat sealing layers of thermoplastic material which comprises progressively passing a filament through a heating zone to preheat said filament to a temperature not lower than the bonding temperature of the layers, and progressively pressing preheated portions of the filament against said layers to cause permanent bonding of said filament and of the underlying layers into a single heat sealed structure in which said filament is at least partially embedded.

6. The method of heat sealing layers of thermoplastic material which comprises first progressively passing a filament through a high frequency field to cause preheating of successive portions of the filament to heat sealing temperature, and thereafter progressively pressing such preheated portions of the filament against said layers to cause bonding of said layers in a linear region in correspondence with the region of pressure in which said filament is at least partially embedded.

7. The method of heat sealing layers of thermoplastic material which comprises progressively passing an electrically conducting filament through a high frequency field to cause preheating of successive portions of the filament to heat sealing temperature, and progressively pressing such preheated portions of the filament against said layers to cause bonding of said layers in a corresponding linear region in Which said filament is at least partially embedded.

8. rThe method of heat sealing layers of thermoplastic material Which comprises progressively passing a filament of dielectric material through a high frequency field to cause preheating of successive portions of the lament to heat sealing temperature, and progressively pressing such preheated portions of the filament against said layers to cause bonding of said layers in a corresponding linear region in which said filament is at least partially embedded.

9. The method of heat sealing layers of thermoplastic material which comprises progressively passing a iilamentary member through a high frequency field to cause preheating of successive portions thereof to heat sealing temperature, and then progressively advancing such preheated portion of said member together with the superimposed layers of said thermoplastic material through the bight of a pair of pressure rolls thereby to cause permanent bonding of said member and of said 1ayers in a corresponding linear region in which said filamentary member is at least partially embedded.

10. The method of heat sealing layers of thermoplastic material which comprises progressively passing a filamentary member of dielectric material through the bight of a pair of electrode rolls between which a high frequency field is maintained to preheat successive portions thereof to hea-t sealing temperature, and immediately thereafter progressively advancing such preheated portion of said member together with layers of said thermoplastic material through the bight of a pair of pressure rolls thereby to cause permanent bonding of said member and of said layers 1n a corresponding linear region in which said filamentary member is at least partially embedded.

11. The method, of heet sealing which cornprises progressively superposing onto layers of relatively low-loss dielectric thermoplastic me terial e lement of relatively high-loss dielectric material to constitute a composite structure, een" iinuously advancing said structure through a high frequency field thereby to raise the temperature of said :filament 'to a 'temperature no1l lower than the bonding temperature of the layers, and proressiveh7 advancing seid preheated structure through a pressure zone thereby to cause transfer oi sealing heat from said filament onto the 10 layers in Contact therewith and permanent bonding of seid filament and of the underlying layers in a corresponding linear region in which said i'ilament is at least; partially embedded.

NICHOLAS LANGER.

References Cited in the file of this patent UNITED STATES PATENTS Name Date Collins Oct. 9, 1951 Number 

1. THE METHOD OF HEAT SEALING LAYERS OF THERMOPLASTIC MATERIAL WHICH COMPRISES BRINGING REGIONS OF THE LAYERS TO BE HEAT SEALED INTO FACE-TOFACE SUPERPOSED POSITION, PREHEATING AN ELONGATED MEMBER TO HEAT SEALING TEMPERATURE IN THE ABSENCE OF CONTACT WITH THE LAYERS TO BE SEALED, AND PRESSING SAID PREHEATED MEMBER AGAINST SAID REGIONS OF THE LAYERS TO CAUSE HEATING AND BONDING OF SAID MEMBER AND OF SAID LAYERS IN SUCH REGIONS. 